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- /*
- NetWinder Floating Point Emulator
- (c) Rebel.COM, 1998
- (c) Philip Blundell 1998-1999
- Direct questions, comments to Scott Bambrough <scottb@netwinder.org>
- This program is free software; you can redistribute it and/or modify
- it under the terms of the GNU General Public License as published by
- the Free Software Foundation; either version 2 of the License, or
- (at your option) any later version.
- This program is distributed in the hope that it will be useful,
- but WITHOUT ANY WARRANTY; without even the implied warranty of
- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
- GNU General Public License for more details.
- You should have received a copy of the GNU General Public License
- along with this program; if not, write to the Free Software
- Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
- */
- #include <asm/asm-offsets.h>
- /* This is the kernel's entry point into the floating point emulator.
- It is called from the kernel with code similar to this:
- mov fp, #0
- teqp pc, #PSR_I_BIT | SVC_MODE
- ldr r4, .LC2
- ldr pc, [r4] @ Call FP module USR entry point
- The kernel expects the emulator to return via one of two possible
- points of return it passes to the emulator. The emulator, if
- successful in its emulation, jumps to ret_from_exception and the
- kernel takes care of returning control from the trap to the user code.
- If the emulator is unable to emulate the instruction, it returns to
- fpundefinstr and the kernel halts the user program with a core dump.
- This routine does four things:
- 1) It saves SP into a variable called userRegisters. The kernel has
- created a struct pt_regs on the stack and saved the user registers
- into it. See /usr/include/asm/proc/ptrace.h for details. The
- emulator code uses userRegisters as the base of an array of words from
- which the contents of the registers can be extracted.
- 2) It locates the FP emulator work area within the TSS structure and
- points `fpa11' to it.
- 3) It calls EmulateAll to emulate a floating point instruction.
- EmulateAll returns 1 if the emulation was successful, or 0 if not.
- 4) If an instruction has been emulated successfully, it looks ahead at
- the next instruction. If it is a floating point instruction, it
- executes the instruction, without returning to user space. In this
- way it repeatedly looks ahead and executes floating point instructions
- until it encounters a non floating point instruction, at which time it
- returns via _fpreturn.
- This is done to reduce the effect of the trap overhead on each
- floating point instructions. GCC attempts to group floating point
- instructions to allow the emulator to spread the cost of the trap over
- several floating point instructions. */
- .globl nwfpe_enter
- nwfpe_enter:
- mov sl, sp
- ldr r5, [sp, #60] @ get contents of PC
- bic r5, r5, #0xfc000003
- ldr r0, [r5, #-4] @ get actual instruction into r0
- bl EmulateAll @ emulate the instruction
- 1: cmp r0, #0 @ was emulation successful
- beq fpundefinstr @ no, return failure
- next:
- .Lx1: ldrt r6, [r5], #4 @ get the next instruction and
- @ increment PC
- and r2, r6, #0x0F000000 @ test for FP insns
- teq r2, #0x0C000000
- teqne r2, #0x0D000000
- teqne r2, #0x0E000000
- bne ret_from_exception @ return ok if not a fp insn
- ldr r9, [sp, #60] @ get new condition codes
- and r9, r9, #0xfc000003
- orr r7, r5, r9
- str r7, [sp, #60] @ update PC copy in regs
- mov r0, r6 @ save a copy
- mov r1, r9 @ fetch the condition codes
- bl checkCondition @ check the condition
- cmp r0, #0 @ r0 = 0 ==> condition failed
- @ if condition code failed to match, next insn
- beq next @ get the next instruction;
- mov r0, r6 @ prepare for EmulateAll()
- adr lr, 1b
- orr lr, lr, #3
- b EmulateAll @ if r0 != 0, goto EmulateAll
- .Lret: b ret_from_exception @ let the user eat segfaults
-
- @ We need to be prepared for the instruction at .Lx1 to fault.
- @ Emit the appropriate exception gunk to fix things up.
- .section __ex_table,"a"
- .align 3
- .long .Lx1
- ldr lr, [lr, $(.Lret - .Lx1)/4]
- .previous
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